Mobile technologies, such as Short Message Service (SMS) texts, have tremendous and untapped potential for disease management in low- and middle-income countries (LMICs). One important example of this involves improving the childhood vaccination series. Immunization is one of the most successful and cost-effective public health interventions, and yet millions of children under the age of one remain under-immunized and at increased risk for premature death, long-term sequelae, and disability due to vaccine-preventable causes. A major barrier to delivering the infant primary series, especially in developing countries, is the difficulty providers have in communicating with parents about the need for and timeliness of these vaccines. Many LMICs do not have functioning preventive health services and well child care, making the delivery of immunizations and other child health programs more difficult. There is an urgent need for interventions that improve communication between health care facilities providing comprehensive child care services (e.g. immunizations) and parents of young children to improve health outcomes (e.g. the timeliness, acceptance, and coverage of vaccinations). Short Message Service (SMS) text messages are an accessible and low-cost means of communication that are widely used globally. Over the past two years, the study team developed and demonstrated the feasibility and consumer acceptability of an SMS immunization reminder system in Guatemala which allowed healthcare workers to collect data on child immunizations and send text message reminders to parents/guardians to attend vaccination appointments. In this proposed exploratory and developmental study, we will optimize, implement, and evaluate an evidence-based centralized method of increasing immunization delivery using a modified version of the SMS reminder/recall system developed by the study team. The project will evaluate the potential for efficacy of our modified centralized approach in two different socio-economic and geographic regions of Guatemala, including a pilot test in Guatemala City where the system was developed and a new introduction in the impoverished southwest Trifinio region where the study team has a well-established and long-term public-private partnership to provide prenatal, maternal, and pediatric care. This study provides an innovative partnership between public, private, and governmental institutions both in the United States and Guatemala that can serve as an important example of supporting international research networks and building research capacity in LMICs. This study has the potential to significantly improve vaccine delivery and coverage with the opportunity for program scalability. Importantly, the technical and administrative infrastructure created by this unique collaboration will be a platform on which the future delivery of other clinical preventive services can be built.